question_answer

A reddish brown colloidal sol is formed when a small amount of \[FeC{{l}_{3}}\] is added to freshly precipitated \[Fe{{(OH)}_{3}}\]. Explain.

Answer:

                \[F{{e}^{3+}}\] ions present in the solution are adsorbed on \[Fe{{(OH)}_{3}}\]. The positively charged particles formed mutually repel and get disintegrated resulting in a reddish brown colloidal sol. \[\underset{\text{(ppt}\text{.)}}{\mathop{Fe{{(OH)}_{3}}}}\,\,\,\,+\,\,\,\underset{\text{(electrolyte)}}{\mathop{F{{e}^{3+}}}}\,\,\,\,\xrightarrow{\,}\,\,\,\,\underset{\text{Colloidal}\,\,\text{sol}\text{.}}{\mathop{[Fe{{(OH)}_{3}}]F{{e}^{3+}}}}\,\] This process of converting a freshly precipitated substance into colloidal solution is called peptisation.